1. Field of the Invention
The present invention relates to a piezoelectric actuator using the piezoelectric effect occurring in a dielectrics made of ceramic, the actuator being used, for example, for a fuel injection pump.
2. Description of the Prior Art
It is known to constitute an actuator to work by the piezoelectric effect of a dielectric made of ceramic, such as Pb Ti O.sub.3 - Pb Zr O.sub.3 (PZT). Generally, the actuator is constituted by laminating a number of dielectric plates, each of which forms, at both of its surfaces, a pair of metallic electrode layers. When laminating the dielectric plates on each other, usually a thin metallic electrode plate is inserted between the plates. In the operation of a piezoelectric actuator, a few hundred volts are applied to the dielectric plates through the metallic electrode plates to create strain in the dielectric plates.
Conventional piezoelectric actuators, however, have several disadvantages. First, there is a problem of flashover both between the actuator and casing and between adjacent metallic electrode plates at an outer periphery of the actuator. When such flashover occurs, the actuator does not expand or contract and cannot effect its pumping or other operation.
Also, expansion or contraction of the piezoelectric plates deforms the metallic electrode plates to some extent due to their elasticity, thus, reducing the amount of displacement of laminated piezoelectric plates. Further, the dielectric plates may be damaged when the thickness of each plate is not uniform or the plates are cambered.